1. Basic Principles of Imaging and Lenses

2. Light

3. Light Photons ElectromagneticRadiation

4. These three are the same… Light *pure energy Electromagnetic Waves *energy-carrying waves emitted by vibrating electrons Photons *particles of light

6. EM Radiation Travels as a Wave c = 3 x 10 8 m/s

8. EM Radiation Carries Energy Quantum mechanics tells us that for photons E = hf where E is energy and h is Planck’s constant. But f = c/ Putting these equations together, we see that E = hc/

9. Electromagnetic Wave Velocity The speed of light is the same for all seven forms of light. It is 300,000,000 meters per second or 186,000 miles per second.

10. The Electromagnetic Spectrum Radio Waves - communication Microwaves - used to cook Infrared - “heat waves” Visible Light - detected by your eyes Ultraviolet - causes sunburns X-rays - penetrates tissue Gamma Rays - most energetic

12. The Multi-Wavelength Sun X-Ray UV Visible Infrared Radio Composite

13. EM Spectrum Relative Sizes

14. The Visible Spectrum Light waves extend in wavelength from about 400 to 700 nanometers.

15. Camera Obscura, Gemma Frisius, 1558 1544 A Brief History of Images

16. http://www.acmi.net.au/AIC/CAMERA_OBSCURA.htmlhttp://www.acmi.net.au/AIC/CAMERA_OBSCURA.html (Russell Naughton) Camera Obscura "When images of illuminated objects... penetrate through a small hole into a very dark room... you will see [on the opposite wall] these objects in their proper form and color, reduced in size... in a reversed position, owing to the intersection of the rays". Leonardo da Vinci Slide credit: David Jacobs

17. Lens Based Camera Obscura, 1568 1558 1568 A Brief History of Images

18. http://brightbytes.com/cosite/collection2.htmlhttp://brightbytes.com/cosite/collection2.html (Jack and Beverly Wilgus) Jetty at Margate England, 1898. Slide credit: David Jacobs

19. Still Life, Louis Jaques Mande Daguerre, 1837 1558 1837 1568 A Brief History of Images

20. Abraham Lincoln? 1558 1840? 1568 A Brief History of Images

21. Silicon Image Detector, 1970 1558 1837 1568 1970 A Brief History of Images

22. 1558 1837 1568 1970 1995 A Brief History of Images Digital Cameras

23. 1558 1837 1568 1970 1995 A Brief History of Images Hasselblad HD2-39 2006

24. Geometric Optics and Image Formation

25. Pinhole Cameras Pinhole camera - box with a small hole in it Image is upside down, but not mirrored left-to-right Question: Why does a mirror reverse left-to-right but not top-to-bottom?

26. Pinhole and the Perspective Projection (x,y) screenscene Is an image being formed on the screen? YES! But, not a “clear” one. image plane effective focal length, f’ optical axis y x z pinhole

27. Problems with Pinholes Pinhole size (aperture) must be “very small” to obtain a clear image. However, as pinhole size is made smaller, less light is received by image plane. If pinhole is comparable to wavelength of incoming light, DIFFRACTION effects blur the image! Sharpest image is obtained when: pinhole diameter Example: If f’ = 50mm, = 600nm (red), d = 0.36mm

28. The Reason for Lenses

29. Image Formation using (Thin) Lenses Lenses are used to avoid problems with pinholes. Ideal Lens: Same projection as pinhole but gathers more light! i o Gaussian Lens Formula: f is the focal length of the lens – determines the lens’s ability to bend (refract) light f different from the effective focal length f’ discussed before! P P’ f

30. Focus and Defocus Depth of Field: Range of object distances over which image is sufficiently well focused, i.e., range for which blur circle is less than the resolution of the imaging sensor. d aperture diameter aperture Gaussian Law: Blur Circle, b Blur Circle Diameter :

31. Problems with Lenses Compound (Thick) Lens Vignetting Chromatic AbberationRadial and Tangential Distortion thickness principal planes nodal points B A more light from A than B ! Lens has different refractive indices for different wavelengths. image plane ideal actual ideal actual

32. Spherical Aberration Spherical lenses are the only easy shape to manufacture, but are not correct for perfect focus.

33. Two Lens System Rule : Image formed by first lens is the object for the second lens. Main Rays : Ray passing through focus emerges parallel to optical axis. Ray through optical center passes un-deviated. image plane lens 2lens 1 object intermediate virtual image final image Magnification: Exercises: What is the combined focal length of the system? What is the combined focal length if d = 0?

34. Lens systems A good camera lens may contain 15 elements and cost a many thousand dollars The best modern lenses may contain aspherical elements

35. http://www.cas.vanderbilt.edu/bsci111b/eye/human-eye.jpg Human Eye The eye has an iris like a camera Focusing is done by changing shape of lens Retina contains cones (mostly used) and rods (for low light) The fovea is small region of high resolution containing mostly cones Optic nerve: 1 million flexible fibers Slide credit: David Jacobs

36. The Eye The human eye is a camera! –Iris - colored annulus with radial muscles –Pupil - the hole (aperture) whose size is controlled by the iris –What’s the “film”? photoreceptor cells (rods and cones) in the retina

37. Human Eye vs. the Camera We make cameras that act “similar” to the human eye

38. Image Formation Digital Camera The Eye Film

39. Insect Eye We make cameras that act “similar” to the human eye Fly Mosquito

40. The Retina

41. Retina up-close Light

42. © Stephen E. Palmer, 2002 Cones cone-shaped less sensitive operate in high light color vision Two types of light-sensitive receptors Rods rod-shaped highly sensitive operate at night gray-scale vision

43. Rod / Cone sensitivity The famous sock-matching problem…

44. Human Eye Rods –Intensity only –Essentially night vision and peripheral vision only –Since we are trying to fool the center of field of view of human eye (under well lit conditions) we ignore rods

45. Human Eye Cones –Three types perceive different portions of the visible light spectrum

46. Human Eye Because there are only 3 types of cones in human eyes, we only need 3 stimulus values to fool the human eye –Note: Chickens have 4 types of cones

47. © Stephen E. Palmer, 2002 Distribution of Rods and Cones Night Sky: why are there more stars off-center?

49. The Physics of Light Some examples of the spectra of light sources © Stephen E. Palmer, 2002

50. More Spectra metamers

51. The Physics of Light Some examples of the reflectance spectra of surfaces Wavelength (nm) % Photons Reflected Red 400 700 Yellow 400 700 Blue 400 700 Purple 400 700 © Stephen E. Palmer, 2002

52. The Psychophysical Correspondence There is no simple functional description for the perceived color of all lights under all viewing conditions, but …... A helpful constraint: Consider only physical spectra with normal distributions area mean variance © Stephen E. Palmer, 2002

53. The Psychophysical Correspondence MeanHue # Photons Wavelength © Stephen E. Palmer, 2002

54. The Psychophysical Correspondence VarianceSaturation Wavelength # Photons © Stephen E. Palmer, 2002

55. The Psychophysical Correspondence AreaBrightness # Photons Wavelength © Stephen E. Palmer, 2002

56. Digital camera A digital camera replaces retina with a sensor array –Each cell in the array is light-sensitive diode that converts photons to electrons –Two common types Charge Coupled Device (CCD) CMOS –http://electronics.howstuffworks.com/digital-camera.htmhttp://electronics.howstuffworks.com/digital-camera.htm

57. CCD Cameras http://huizen.ddsw.nl/bewoners/maan/imaging/camera/ccd1.gif Slide credit: David Jacobs

58. Sensor Array CMOS sensor

59. Sampling and Quantization

60. Interlace vs. progressive scan http://www.axis.com/products/video/camera/progressive_scan.htm

61. Progressive scan http://www.axis.com/products/video/camera/progressive_scan.htm

62. Interlace http://www.axis.com/products/video/camera/progressive_scan.htm

63. Color Sensing in Camera (RGB) 3-chip vs. 1-chip: quality vs. cost Why more green? http://www.coolditionary.com/words/Bayer-filter.wikipedia http://www.cooldictionary.com/words/Bayer-filter.wikipedia Why 3 colors?

64. Practical Color Sensing: Bayer Grid Estimate RGB at ‘G’ cels from neighboring values http://www.cooldictionary.com/ words/Bayer-filter.wikipedia

65. Image Formation f(x,y) = reflectance(x,y) * illumination(x,y) Reflectance in [0,1], illumination in [0,inf]

66. White Balance White World / Gray World assumptions

67. Problem: Dynamic Range 1500 1 1 25,000 400,000 2,000,000,000 The real world has High dynamic range

68. pixel (312, 284) = 42 Image 42 photos? Is Camera a photometer?

69. Long Exposure 10 -6 10 6 10 -6 10 6 Real world Picture 0 to 255 High dynamic range

70. Short Exposure 10 -6 10 6 10 -6 10 6 Real world Picture 0 to 255 High dynamic range

71. sceneradiance (W/sr/m )  sensorirradiancesensorexposure LensShutter 2 tttt analog voltages digital values pixel values CCDADCRemapping Image Acquisition Pipeline Camera is NOT a photometer!

72. Varying Exposure

73. What does the eye sees? The eye has a huge dynamic range Do we see a true radiance map?